In a conventional distribution board, for example, as disclosed in Japanese Utility Model Laid-Open S63-29310 (Patent Document 1), a three-phase four-wire distribution board having four vertical bus-lines is known.
In general, as a DC power supply distribution board, the structure illustrated in FIGS. 5A and 5B is known. That is to say, two units on which two respective breakers 2a and 2b arranged in the left and right sides are mounted are horizontally disposed; for the two respective units, two pieces each of vertical bus-lines 3 and 4, i.e., totally four vertical bus-lines are provided so that the two units can individually be inserted or removed. The vertical bus-lines 3 and 4, four in number are arranged in a limited space inside the distribution board; in order to secure an insulation distance between the vertical bus-lines 3 and 4, flat conductors are adopted.
The left and right breakers 2a and 2b are provided with protection covers 1a and 1b, respectively; the vertical bus-lines include the vertical bus-lines 3 for the left unit and the vertical bus-lines 4 for the right unit. The vertical bus-line 3 for the left unit is connected with a left-side contactor 5, and the vertical bus-line 4 for the right unit is connected with a right-side contactor 6. The left-side contactor 5 that is included in the left unit and is connected with the vertical bus-line 3 is mounted on a left unit base 7; the right-side contactor 6 that is included in the left unit and is connected with the vertical bus-line 4 is mounted on a right unit base 8.    [Patent Document 1] Japanese Utility Model Laid-Open S63-29310 (FIGS. 1 and 2)